Catalytic process for the modification of carbohydrates, alcohols, aldehydes or polyhydroxy compounds

ABSTRACT

The invention relates to the industrial conversion of carbohydrates, alcohols, aldehydes or polyhydroxy compounds in aqueous phase. According to the invention a catalytic method is used for the conversion, using a metal catalyst consisting of polymer-stabilized nanoparticles. A catalyst of this type is not deactivated by the conversion reaction as long as the stabilizing interaction between the polymer and the nanoparticles is maintained.

[0001] Description

[0002] The invention relates to a process for the industrial conversionof carbohydrates, alcohols, aldehydes or polyhydroxy compounds inaqueous phase.

[0003] In many industrial processes, the conversion, e.g. the oxidation,of carbohydrates, alcohols, aldehydes or polyhydroxy compounds inaqueous phase plays a decisive role and often forms the critical stageof synthesis processes.

[0004] Thus, for example, the D-gluconic acid required for manyindustrial applications is prepared by an oxidation of D-glucose, whichis carried out as a microbial oxidation using Aspergillus niger.

[0005] A further important oxidation is the formation of2-keto-L-gulonic acid from sorbose as intermediate step in thepreparation of ascorbic acid (vitamin C). The classical Reichsteinprocess here provides a 2-stage reaction in which, in a complex manneran L-sorbofuranose is formed, which is then oxidized to 2-keto-L-gulonicacid, for example by an electrochemical method or catalytically usingnickel oxide.

[0006] The hydrogenation of reducing mono- and disaccharides withsupported noble metal catalysts is described in DE 19523008 A1. Forindustrial production, i.e. on a large scale designed for largeconversions, such catalysts are, however, unsuitable, meaning that Raneynickel catalysts generally have to be used on an industrial scale.

[0007] During the reductive amination of reducing sugars withalkylamines to give alkylaminopolyols, use is normally made of Raneynickel catalysts. One disadvantage of these catalysts is the very shortservice life (dissertation by M. Schüttenhelm, 1995, TU Braunschweig),meaning that industrial conversion has hitherto been unsuccessful due tohigh catalyst costs. In addition, during the further work-up, dissolvedor complexed Ni constituents, which permit the further use of theresulting product only through use of downstream complex andcost-intensive cleaning processes, must be taken into account.

[0008] Alternatively, the preparation of these products with supportedPd catalysts has been investigated. Here, a loss of metal was foundwhich, firstly, considerably reduced the activity of the catalyst and,because of the economic considerations, prevents its use (dissertationby R. Cartarius, 1999, TU Darmstadt).

[0009] It is therefore in principle known, e.g. from EP 0 201 957 A2, WO97/34861, U.S. Pat. No. 5,643,849 or tetrahedron letters 38 (1997),9023-9026, to carry out such reactions, in particular oxidations,catalytically, in particular using noble metal catalysts, mild reactionconditions with regard to the pH and the reaction temperature being madepossible. Particularly suitable catalyst metals here are platinum, butalso palladium and possibly rhodium, all noble metals in principle beingsuitable, taking into consideration their activity and their oxygentolerance.

[0010] The industrial use of the theoretically possible catalyticoxidation has, however, hitherto failed due to deactivation phenomena ofthe catalysts (cf. Mallat, Baiker ‘Oxidation of alcohols with molecularoxygen on platinum metal catalysts aqueous solutions’ in Catalysis Today19 (1994), pp. 247-248). The deactivation of the catalysts is attributedhere to the formation of catalyst poisons, an overoxidation of the noblemetal surface and to a surface corrosion and restructuring of the noblemetal. Since some of the deactivation effects of the catalyst areirreversible and cannot therefore be rectified by a regeneration, theindustrial application fails due to the low service life of thecatalysts and the high use of noble metal material required therewith,which makes the process uneconomical. The metal detachment which arisesbecause of the deactivation effects causes not only high costs for thenoble metal used, but also leads to contamination of the catalyticallyprepared product.

[0011] A proposed use of noble metal catalysts provided with promotermetals has produced a certain reduction in the irreversible deactivationeffects, but still falls a long way short of making catalytic oxidationprocesses economically competitive with processes used hitherto.

[0012] The serious deactivation effects for carrying out an oxidationreaction have therefore led to the use of noble metal catalysts inpractice only for carrying out reactions which are not very aggressivewith regard to deactivation, in particular for hydrogenation reactions.For the further development of the catalysts for this purpose,enlargement of the catalyst surface by the formation of fine noble metalparticles has been carried out by preparing the catalyst from a colloid.The particles are separated from one another and prevented from cakingby providing the colloid with a suitable polymer such that the particlesare surrounded by a polymer sheath. In this connection, attempts havealso been made to reduce the susceptibility of the metal particlesurfaces toward deactivation, for example by catalyst poisons. For thisreason, for hydrogenation reactions of small molecules in which thereaction proceeds without diffusion limitation, metal catalysts havebeen used which have been formed from polymer-protected Pt or Pdparticles.

[0013] For example, Chem. 1 ng. Technik 69 (1997), 100-103 disclosessupported palladium catalysts in millimeter-sized gelatinous polymernetworks for reducing nitrite. Nitrite is a very small molecule in whichthe reduction proceeds without diffusion limitation. Hydrogenationreactions with metal catalysts which have been formed frompolymer-protected Pt or Pd particles are not disclosed in the prior artfor the conversion of relatively large molecules, such as, for example,carbohydrates.

[0014] To ensure uniform distribution of the particles, it has also beenproposed to surround the particles with surfactants in order to achievea uniform distribution upon application to a support. In thistechnology, however, the surfactant sheath is dissolved followinguniform distribution of the particles in order to achieve the catalysteffect, meaning that the sole function of the surfactant is to achieveuniform distribution.

[0015] It has also been proposed to form polymer-protected particlecatalysts as bimetal or even trimetal catalysts. While the combinationof noble metals serves as a selectivity control, the combination ofnoble metal with one or two promoter metals is successful in reducingthe deactivation of the catalysts. As a result, perspectives for apractical application of a catalytic process have been opened up for thehydrogenation reaction and possibly other reducing reactions. Oxidation,which is significantly more aggressive with regard to deactivation ofthe catalyst, has not been investigated further in this respect due tothe existing unpromising situation.

[0016] For the reactions of the generic type, recourse must therefore befurther made to the known processes which are aggressive with regard toenvironmental influences or can only be controlled by very involvedmeans, although considerable efforts have been made to arrive atprocesses which are simpler and proceed under milder reactionconditions.

[0017] Starting from the endeavor to provide an industrially applicableprocess for the conversion, in particular oxidation, hydrogenation orreductive amination, of carbohydrates, alcohols, aldehydes orpolyhydroxy compounds in aqueous phase, which proceeds under milderreaction conditions, it is envisaged according to the invention that theconversion be carried out catalytically using a metal catalyst formedfrom polymer-stabilized nanoparticles.

[0018] The present invention is based on the finding, which iscompletely surprising and unexpected for the specialist world, thatmetal catalysts formed from polymer-stabilized nanoparticles are notdeactivated during the catalytic conversion, in particular oxidation,hydrogenation or reductive amination, of carbohydrates, alcohols,aldehydes or polyhydroxy compounds in aqueous phase, provided thestabilizing interaction between polymer and nanoparticles is retained.In this connection, it is not necessary according to the invention thata promoter metal is added to the noble metal catalyst, even if this isnaturally self-evidently possible in this process according to theinvention. It is also surprising for the person skilled in the art thatthe known metal catalysts formed from polymer-protected particles forhydrogenation reactions for large molecules, such as carbohydrates andothers, can be used, for which the person skilled in the art would haveexpected a diffusion limitation. The catalytic conversion ofcarbohydrates with these catalysts surprisingly proceeds despite thepolymer matrix surrounding the active centers with high reaction ratesand selectivities. The person skilled in the art would have expectedthat, compared with the known reactions with nitrite, the largecarbohydrate molecules would be available for a reaction only to alimited extent due to the polymer matrix surrounding the active centeror due to diffusion limitation. However, it could be shown that even thelarge di- and oligosaccharide molecules can advantageously be convertedusing the catalyst system according to the invention.

[0019] The present invention relates in particular to processes for theindustrial conversion of starting materials, chosen from the groupconsisting of alcohols, aldehydes and/or polyhydroxy compounds, such ascarbohydrates, carbohydrate derivatives, starch hydrolysates, inparticular mono-, di- or trisaccharides, in aqueous phase, where theconversion is carried out catalytically using a metal catalyst formedfrom polymer-stabilized nanoparticles. It may be provided also tojointly convert mixtures of said starting materials.

[0020] In a preferred embodiment of the present invention, theconversion is an oxidation of said starting materials, carbohydrates,for example glucose, sorbose, sucrose, maltose, lactose, starchhydrolysates and/or isomaltulose preferably being oxidized to thecorresponding carbohydrate acids. Because of the very aggressiveconditions during oxidations, the long-term stability observed accordingto the invention and the metal leaching which does not arise in thisembodiment are particularly surprising.

[0021] In a further embodiment, the conversion is a reduction, inparticular a hydrogenation, reducing sugars, such as, for example,glucose, fructose, xylose, sorbose, isomaltose, isomaltulose,trehalulose, maltose and/or lactose, being hydrogenated to give thecorresponding sugar alcohols. In this way, it is possible, for example,to obtain isomalt, 1,1-GPM (1-O-α-D-glucopyranosyl-D-mannitol) or1,6-GPS (6-O-α-D-glucopyranosyl-D-sorbitol) enriched mixtures fromisomaltulose. Such enriched mixtures are described in DE 195 31 396 C2.

[0022] In a further embodiment, the industrial conversion of saidstarting materials can be a reductive amination, preference being givento reductively aminating reducing sugars, in particular glucose,fructose, xylose, sorbose, isomaltose, isomaltulose, trehalulose,maltose and/or lactose.

[0023] In a preferred embodiment, the metal catalyst is a catalyst whichessentially consists of noble metal or comprises the latter, where thenoble metal can, for example, be platinum, palladium, rhodium and/orruthenium. However, the metal catalyst can also be a catalyst whichessentially consists of a base metal or comprises the latter, where thebase metal can, for example, be copper and/or nickel.

[0024] In connection with the present invention, the conversion takesplace in aqueous phase, the conversion preferably taking place at atemperature of from 35-120° C. and a pH of from 5 to 12.

[0025] In connection with the present invention, a polymer-stabilizednanoparticle is understood as meaning a metal particle around which apolymer sheath is formed, where the total diameter of the polymer-coatedmetal particle, as metal particle core plus sheath, is preferably in arange from 3 to 200 nanometers.

[0026] The invention provides in a particularly preferred manner thatthe alcohols, aldehydes or polyhydroxy compounds to be reacted, inparticular carbohydrates, carbohydrate derivatives or the like areconverted in aqueous solution, concentrations of from 0.1 to 60% beingpreferred. For example, the glucose may be present in the form ofglucose syrup.

[0027] In particular, in a further preferred embodiment, it may beprovided to pass the products mentioned above converted according to theinvention during the oxidation following their conversion to a productsolution to an electrodialysis, and in so doing to remove and obtain theproducts from the resulting product solution. A particularly preferredprocedure of this type is suitable, for example, for the preparation ofmonooxidized carbohydrates or carbohydrate derivatives and primaryalcohols. Separating off the oxidation products by means ofelectrodialysis, for example as described in EP 0 651 734 B1, leads tovirtually pure products being obtained.

[0028] The process according to the invention can thus be coupled in apreferred manner with a process and the appertaining equipment accordingto EP 0 651 734 B1 in order to obtain the desired products in aparticularly pure form by means of electrodialysis. The teaching of EP 0651 734 B1 is incorporated in its entirety into the disclosure contentof the present teaching with regard to the electrodialysis separationdescribed therein, and protection is also sought therefor.

[0029] If the catalyst particles according to the invention arecontinually used repeatedly, it must be taken into consideration thatthe polymer sheath around the nanoparticles is detached or consumed.According to the invention, it is therefore particularly preferred ifthe polymer stabilizing the nanoparticles is added to the aqueous phasecontinuously or at suitable time intervals in order, in this way, toensure that the effective polymer sheath around the nanoparticles isretained.

[0030] In the process according to the invention, the nanoparticles canbe immobilized in a manner known per se on a support material, i.e.supported, the support material used preferably being a porous materialin continuous form or in powder form, or the polymer-stabilizednanoparticles are immobilized in a gel structure.

[0031] Suitable immobilization materials with the help of adsorptionare, in particular: Al₂O₃, SiO₂, TiO₂, ZrO₂, activated carbon, polymerlatex, polystyrene latex, polyacrylamide gel, Deloxan (alkylsulfonicacid polysiloxane, aminoethyl Bio-Gel P-150. Inclusion immobilizationcan take place in a preferred embodiment in alginates,polyvinyl-alcohol, polyurethanes or the like.

[0032] If, in one embodiment of the invention, supported catalystsimmobilized as described above are used, the polymer-stabilized and/orsupported nanoparticles according to the invention can preferably behomogeneously or inhomogeneously distributed in gels, particularlyhydrogels, or else be localized on the surface. As well as the supportmaterials aluminum oxide, silicon dioxide and/or titanium dioxide, alsosuitable for this purpose are activated carbon, alumosilicates and ionexchange resins or the like.

[0033] Finally, in a further embodiment, membrane arrangements are alsopossible in which the active component, i.e. the polymer-stabilizednanoparticles, optionally also in supported form, are applied to orbetween membranes (for example hollow fibers, diffusion membranes,porous membranes and flat membranes).

[0034] In a preferred embodiment, suitable polymers for protecting andcoating the nanoparticles are numerous homopolymers, copolymers and, inparticular, block copolymers and graft copolymers. Particular mentionmay be made of polyvinyl pyrrolidones and suitable derivatives,polyvinyl alcohol, polyacrylic acid, poly(2-ethyl-2-oxazoline),poly(2-hydroxy-propyl methacrylate), poly(methyl vinyl ether-co-maleicanhydride), polymethacrylic acid, poly(1-vinylpyrrol-idone-co-acrylicacid), poly(styrenesulfonic acid),poly(2-acrylamido-2-methyl-1-propanesulfonic acid),poly-(vinylphosphonic acid), polydiallyldimethylammonium chloride(PDADMAC), polymethacrylamidopropyltrimethylammonium chloride, poly(3-chlorohydroxypropyl-2-methacryloxyethyldimethyl-ammonium chloride).

[0035] The catalysts according to the invention can be used, in apreferred embodiment, also as colloids/clusters, the active componentbeing in the form of free, i.e. not immobilized, colloids or clusters.The largest arrangement of these colloids/clusters is, according to theinvention, in the nanometer range, i.e. in a range from 1 nm to 20 nm.It is only essential that the colloid particles and clusters aresurrounded by a protecting polymer sheath.

[0036] The catalysts can be designed according to the type of catalystand the reactor in question, for example as spheres, beads, cylinders,hollow cylinders, meshes, powders, pressed articles, granules, hollowspheres, fibers and films. The process itself can be used in plantswhich operate continuously, semicontinuously or else batchwise.Depending on the catalyst used, suitable reactors are, for example,fixed-bed reactors, reactors with expanding fixed beds, moving-bedreactors, fluidized bed reactors, stirred-bed reactors, stirred tankreactors and membrane reactors. These systems can be operated with orwithout catalyst and/or liquid recycling. These systems can, ifnecessary, also be provided with suitable internals for catalystretention, for example with cyclones, filters and membranes.

[0037] Further advantageous embodiments arise from the dependent claims.

[0038] The invention is illustrated in more detail by reference to theexamples below and the appertaining figures.

[0039] The figures show

[0040]FIG. 1: Measurement results for the oxidation of sorbose using acatalyst used according to the invention,

[0041]FIG. 2: Measurement results for the oxidation of sorbose using acomparison catalyst,

[0042]FIG. 3: Measurement results for the oxidation of sorbose using acatalyst used according to the invention,

[0043]FIG. 4: Measurement results for the oxidation of glucose using acatalyst used according to the invention,

[0044]FIG. 5: Measurement results for oxidation of sucrose using acatalyst used according to the invention and a comparison catalyst,

[0045]FIG. 6: Measurement results for the reductive amination ofisomaltulose using a catalyst used according to the invention and acomparison catalyst,

[0046]FIG. 7: Measurement results for the hydrogenation of isomaltuloseusing a catalyst used according to the invention and a comparisoncatalyst.

EXAMPLE 1

[0047] Preparation of PVP-Stabilized Platinum Colloids

[0048] 3.27 g of polymer, namely polyvinylpyrrolidone (PVP), aredissolved in 33 ml of methanol, it possibly being necessary to gentlyheat the solution so that the polymer dissolves completely. Followingdissolution of the polymer, 398.2 mg (0.769 mmol) of hydrogenhexachloroplatinate(IV) hydrate (H₂PtCl₆.6H₂O) (platinum content 150 mg)and 291.6 mg (7.29 mmol) of NaOH are added thereto and the mixture isboiled under reflux. The solution also turns yellow during thisoperation upon the addition of hydrogen hexachloroplatinate(IV) hydrate.Following reduction, the mixture is boiled under reflux for a further 60minutes. The reduction takes place suddenly only after boiling for about30 minutes. The reduction is also evident here from the formation of abrown-black colloidal sol. After the sol has cooled, the unreactedalcohol is removed dialytically. During the dialysis, the colloidal solis continuously circulated by pump through the intracapillary volume ofa hollow fiber dialysis module (Fresenius model F5 HPS) incountercurrent to deionized water in the extracapillary volume. Duringdialysis, all of the colloidal sol is retained.

EXAMPLE 2

[0049] Supporting the Pt Colloid on Al₂O₃

[0050] 4.69 g of Al₂O₃ (HL 1000) in the form of highly porous particlesare added to a colloidal solution comprising 50 mg of Pt. 1.15 ml offormic acid are then added and the mixture is stirred overnight. Thesolution becomes clear over the course of time. The reaction mixture isfiltered over a G4 frit. The solid is washed first with methanol andthen with distilled water and dried in a drying cabinet.

EXAMPLE 3

[0051] Sorbose Oxidation

[0052] To determine the sorbose degradation activity, the reactor isfilled with 150 ml of catalyst suspension. Prior to the feeds, thereaction suspension is gassed for 30 minutes with hydrogen in order toexpel other gases, primarily oxygen, from the reaction solution and inorder to activate the catalyst. To strip the dissolved hydrogen from thereaction suspension, the solution is gassed with nitrogen for about 15minutes. Under nitrogen blanketing, 7.5 g of sorbose are added to thesolution, and the mixture is heated to a reaction temperature of 50° C.The pH is then adjusted to 7.3. After the reaction suspension hasreached 50° C., it is then gassed with oxygen, i.e. the reaction isthereby started, the gassing rate at the start being very high so thatrapid saturation of the reaction suspension is achieved. After completesaturation (about 95%) has been achieved, the gassing rate is reduced.The degree of saturation is monitored using the oxygen electrode, andthe gassing rate is increased again where necessary so that the reactionremains saturated over the entire course of the reaction. The reactiontime was 24 hours per feed. The catalyst was then subjected to theregeneration treatment mentioned and is then prepared for the next feed.

EXAMPLE 4

[0053] Comparative Experiment

[0054] For the sorbose oxidation shown in example 3, thepolymer-protected platinum colloid catalyst prepared according toexample 1 and 2 has been investigated with regard to its activity inrepeated reaction runs. The measurement results obtained therein areshown in FIG. 1 and show that the activity of the catalyst remainsvirtually unchanged over many feeds (of 24 hours in each case), while atraditional platinum catalyst on Al₂O₃ has an activity which is reducedto 20 to 30% following comparable feeds, as FIG. 2 shows. Using atomicabsorption spectroscopy, it has been established that the traditionalplatinum catalyst had lost 28% platinum after just 6 feeds, while thecatalyst according to the invention had no losses.

EXAMPLE 5

[0055]FIG. 3 illustrates the activity course for a catalyst according tothe invention analogous to FIG. 1, where the regenerating gassing withhydrogen according to example 3, which has been carried out in otherrespects, has been omitted, as a result of which the activity has beenconsiderably reduced during the eleventh feed. However, by subsequentlycarrying out gassing with hydrogen, the original activity is restored,as is evident at the twelfth feed according to FIG. 3. Deactivationwithout regeneration treatment is therefore reversible.

EXAMPLE 6

[0056] Glucose Oxidation

[0057] To determine the glucose degradation activity, the reactor isfilled with 100 ml of catalyst suspension. Prior to the feeds, thereaction suspension is gassed with nitrogen for 15 minutes in order toexpel other gases, primarily oxygen, from the reaction solution. Undernitrogen blanketing, 10 g of glucose are added to the solution, and themixture is heated to a reaction temperature of 50° C. The pH is thenadjusted to 9.5. After the reaction suspension has reached 50° C., it isthen gassed with oxygen, i.e. the reaction is thereby started, thegassing rate at the start being very high in order to achieve rapidsaturation of the reaction suspension. After complete saturation (about95%) has been reached, the gassing rate is reduced. The degree ofsaturation is monitored using the oxygen electrode, and the gassing rateis increased again where necessary so that the reaction remainssaturated over the entire course of the reaction. FIG. 4 shows that theactivity of the catalyst at worst decreases slightly after a few feedsof 4 hours each, while traditional catalysts are virtually unusableafter no more than 4 feeds because the activity has dropped to 20% orbelow.

EXAMPLE 7

[0058] Preparation of Polymer-Stabilized Metal Colloids TABLE 1Qualitative composition of catalysts 1 to 5 Active Stabilizing Type ofmetal Support polymer conversion Catalyst 1 Pt Al₂O₃ Polyvinyl-Oxidation pyrrolidone Catalyst 2 Pd TiO₂ Poly(1-vinyl- Reductivepyrrolidone)- amination co-acrylic acid Catalyst 3 Ru Al₂O₃ Polyvinyl-Hydrogena- pyrrolidone tion Catalyst 4 Cu Activated Polyvinyl-Hydrogena- carbon pyrrolidone tion Catalyst 5 Ni TiO₂ Polymethacryl-Hydrogena- amidopropyl- tion trimethyl- ammonium chloride

[0059] The polymer-stabilized metal colloids were prepared analogouslyto example 1. The composition of the catalyst is given in table 1. Theuse amount of the polymer used in each case was here initially keptconstant. The amount of noble metal acids or metal salts used was chosensuch that, following theoretical complete conversion, a catalyticallyactive metal content of 150 mg can be assumed. Table 2 shows the rawmaterials and amounts for the preparation of the catalysts. TABLE 2Quantitative composition of catalysts 1 to 5 Amount of Active Startingstarting Amount in metal component component in mg mmol Catalyst PtH₂PtCl₆.6 398.2 0.769  1* H₂O Catalyst Pd PdCl₂ 249.9 1.41 2 Catalyst RuRuCl₃ 307.9 1.48 3 Catalyst Cu CuCl₂ 319.7 2.36 4 Catalyst Ni Ni (NO₃)₂466.9 2.56 5

[0060] The catalysts were supported analogously to the procedure givenin example 2.

EXAMPLE 8

[0061] Oxidation of Sucrose

[0062] The oxidation of sucrose using catalyst 1 is carried out inaccordance with example 3.

[0063] The reaction temperature here is 40° C., and an electrodialysisunit is used to continuously separate off the oxidation products(described in detail in the dissertation by M. Schüttenhelm, TUBraunschweig and in EP 0 651 734 B1) The unit was operated for 10 daysand produced the following product spectrum:

[0064] 1-O-(β-D-fructosylfuranuronyl)-α-D-glucopyranoside: 36±3%

[0065] 2-O-(α-D-glucopyranosyl)-β-D-glucofuranonic acid: 37±3%

[0066] 1-O-(β-D-fructosylfuranosyl)-α-D-glucopyranuronide: 10±2%

[0067] Other products which could not be characterized further: 5±2%

[0068] The activity of the catalyst was virtually constant over 10 days.

[0069] As a comparison, a non-polymer-stabilized commercially availablecatalyst containing Pt on an activated carbon support and having a metalcontent of 1% by weight was tested and produced the following productspectrum:

[0070] 1-O-(β-D-fructosylfuranuronyl)-α-D-glucopyranoside: 37±3%

[0071] 2-O-(α-D-glucopyranosyl)-β-D-glucofuranonic acid: 36±3%

[0072] 1-O-(β-D-fructosylfuranosyl)-α-D-glucopyranuronide: 10±2%

[0073] Other products which could not be characterized further: 13±2%

[0074] As well as the desired monosucrose carboxylic acids, thiscomparison catalyst produced a considerably higher proportion ofbyproducts, as FIG. 5 shows. Even after the third day it was possible toobserve a continuous decrease in catalyst activity.

EXAMPLE 9

[0075] Reductive Amination of Isomaltulose (Palatinose) in theSuspension Process

[0076] The investigations for the reductive amination were carried outin a high-pressure autoclave in a slurry process using catalyst 2 (cf.Ex. 7) (5 g).

[0077] The catalytic hydrogenations were carried out in a laboratoryhigh-pressure autoclave with the following operating data:

[0078] Autoclave

[0079] 750 ml high-pressure autoclave, thermostatable; max. operatingpressure: 15 Mpa (BERGHOF, Eningen)

[0080] speed-controlled, inductively operated stirrer

[0081] internal temperature measurement by PT 100 resistant thermometer

[0082] manual sampling needle valve

[0083] Thermostat:

[0084] Compact low-temperature thermostat RKS 20 D with external controlunit (LAUDA, Lauda-Königshofen)

[0085] Introduction of Hydrogen:

[0086] Removal from cylinders via pressure-reducing valves:

[0087] <10 Mpa: flushing unit; 15 Mpa: reaction connection

[0088] Amination with n-dodecylamine:

[0089] 50 g (0.139 mmol) of palatinose monohydrate(M_(r)[C₁₂H₂₂O₁₁H₂O]=360.31 g/mol) were dissolved in a mixture of 180 mlof water and 55 ml of 2-propanol in a thermostatable 55 ml double-walledflask, and cooled to 10° C. A solution of 7.36 g (0.040 mol) ofn-dodecylamine (M_(r)[C₁₂H₂₇N]=185.35 g/mol) in 120 ml of water and 70mol of 2-propanol was slowly added dropwise thereto, and the mixture wasstirred well for 1 h. The resulting osylamine reaction solution wastransferred to the heated autoclave, and mixed with the catalyst, thenflushed rapidly three times with hydrogen and hydrogenated for 24 h at50 bar and 70° C. After cooling to room temperature, the catalyst wasfiltered off and the crude product solution was carefully concentratedon a rotary evaporator at 38° C. in a water-jet vacuum. The residue wasthen purified.

[0090] It was found that the hydrogen partial pressure during thehydrogenation should, in a preferred embodiment, be at least 30 bar inorder to suppress undesired secondary reactions. It is of course alsopossible to carry out the hydrogenation at 180 bar or above. Theexperiments were all carried out at 50 bar and a temperature of 70° C.

[0091] The plant was operated batchwise for 10 days and filled with newstarting material solution every 24 hours. The catalyst was not changedduring this time. As a comparison, a non-polymer-stabilized catalyst (1%Pd on TiO₂) was tested. The activity was assessed by determining theisomaltulose conversion in each case after 24 hours. At the start, theconversion was virtually quantitative for the two catalysts (red.substances <0.1%, therefore below the detection limit); this value waschosen, as 100%, to be the reference parameter for the evaluation of theexperimental series.

[0092] The results are shown in FIG. 6.

[0093] The non-polymer-stabilized support loses 15% of its reactivityafter just the third day in this reaction; the reactivity of thepolymer-stabilized catalyst remains virtually unchanged throughout theinvestigated period.

Example 10

[0094] Hydrogenation Experiments

[0095] Within the scope of the investigations, the suitability ofpolymer-stabilized catalysts for hydrogenation reactions wasinvestigated.

[0096] In each case, 5 g of catalysts 3-5 were prepared and tested inthe autoclave system described above with the sugar isomaltulose. Forthis, 500 ml of isomaltulose solution with a dry-substance content of30% were in each case introduced into the autoclaves, and 5 g of thecatalyst were added. As comparison catalyst, an Ni/SiO₂-based standardcatalyst was used. The autoclave was sealed and flushed three times withnitrogen to remove the oxygen. The subsequent 10 batch hydrogenationsfor each catalyst were carried out at the following parameter settings:Reaction temperature:  70° C. Hydrogen partial pressure: 150 bar Stirrerspeed: 700 rpm Reaction time:  24 h

[0097] The hydrogenation of isomaltulose produces, as main products, apolyol isomer mixture consisting of 6-O-α-D-glucopyranosyl-D-sorbitol(1,6-GPS) and 1-O-α-D-glucopyranosyl-D-mannitol (1,1-GPM). The activitywas assessed by determining the isomaltulose conversion after 24 hours.FIG. 7 shows that in the case of catalysts 3 to 5, no reduction inreactivity is observed during the period of investigation, while in thecase of the comparison catalyst, a decrease in reactivity is observedeven from the 5th hydrogenation.

[0098] Depending on the metal used and support for the catalysts used,it is possible to selectively control the quantitative ratio with regardto the 1,6-GPS and 1,1-GPM proportion of the product solutions. As table3 shows, the selectivity of the hydrogenation reaction can be influencedthrough the choice of catalyst in such a way that targeted preparationof an appropriately 1,6-GPS and 1,1-GPM enriched product solution ispossible. TABLE 3 Selectivity of the hydrogenation reaction CatalystSelectivity Catalyst 3 1, 6-GPS-selective Catalyst 4 1, 1-GPM-selectiveCatalyst 5 equimolar ratio Comparison catalyst equimolar ratio

[0099] The examples given demonstrate that, despite varying combinationsof different metals, polymers and supports, a large number ofprincipally identical catalysts can be prepared which have the commonfeature that, particularly in an aqueous medium, they have asignificantly higher ability with regard to adhesion and loading of theactive metal component and thus longer service lives than traditionallyused catalysts.

1. A process for the industrial conversion of carbohydrates, alcohols,aldehydes or polyhydroxy compounds in aqueous phase, which comprisescarrying out the conversion catalytically using a metal catalyst formedfrom polymer-stabilized nanoparticles.
 2. The process as claimed inclaim 1, where the conversion is an oxidation.
 3. The process as claimedin claim 2, where glucose, fructose, sorbose, sucrose and/orisomaltulose is oxidized.
 4. The process as claimed in claim 1, wherethe conversion is a hydrogenation.
 5. The process as claimed in claim 4,where reducing sugars are hydrogenated, in particular glucose, fructose,xylose, sorbose, isomaltose, isomaltulose, trehalulose, maltose and/orlactose.
 6. The process as claimed in claim 1, where the conversion is areductive amination.
 7. The process as claimed in claim 6, wherereducing sugars are reductively aminated, in particular, glucose,fructose, xylose, sorbose, isomaltose, isomaltulose, trehalulose,maltose and/or lactose.
 8. The process as claimed in any of claims 1 to7, where the metal is a noble metal, e.g. platinum, palladium, rhodiumand/or ruthenium.
 9. The process as claimed in any of claims 1 to 7,where the metal is a base metal, in particular, copper and/or nickel.10. The process as claimed in claim 8 or 9, wherein the metal catalystused is a monometal catalyst.
 11. The process as claimed in claim 8 or10, wherein the noble metal catalyst comprises platinum or a platinumalloy.
 12. The process as claimed in any of claims 8 to 11, wherein themetal catalyst comprises at least two metals.
 13. The process as claimedin any of claims 8 to 12, where the metal catalyst has at least onepromoter metal.
 14. The process as claimed in any of claims 1 to 13,wherein the nanoparticle-stabilizing polymer is added to the aqueousphase continuously or at suitable time intervals.
 15. The process asclaimed in any of claims 1 to 14, wherein the metal catalyst used ispolymer-stabilized nanoparticles held in a membrane arrangement.
 16. Theprocess as claimed in any of claims 1 to 14, wherein the metal catalystused is polymer-stabilized nanoparticles immobilized on a supportmaterial.
 17. The process as claimed in claim 16, wherein thepolymer-stabilized nanoparticles are immobilized in a gel structure. 18.The process as claimed in any of claims 1 to 3 and 8 to 17, where theproducts obtained during the oxidation are removed and obtainedcontinuously from the reaction system by means of electrodialysis.